On construction jobsites, there is a need for locating points of interest on two-dimensional horizontal surfaces. A simple, accurate and cost effective system for the layout of floor plans at the jobsite has long been in need. Conventional GPS is not usable inside standard steel construction buildings, and previous laser based systems have been overly complex and expensive.
Two earlier patent documents have advanced the art in this area in a significant way, disclosing a laser system that provides the elements for visually locating points of interest on a two-dimensional horizontal surface. A pair of “base units” are placed on the jobsite surface, and these base units have certain capabilities that are described in those earlier patent documents. One of these documents is U.S. Pat. No. 8,087,176; a second such document is published application number US 2012/0203502; both patent documents are commonly-assigned to Trimble Navigation Limited.
The published application teaches using a fan beam, consisting of modulated laser light that is emitted by a first base unit. The base units have a “null-position” photosensor that can delineate horizontal positioning, and can help aim the fan beam until it is directly striking the center portion of a second base unit. The goal is to adjust the aim of the fan beam of the first base unit until it strikes directly at the centerline of the horizontal-sensitive (null-position) photosensor on the second base unit. This procedure is used in establishing an alignment axis between the two base units.
It would be beneficial to have an omnidirectional photosensor on each base unit, to help begin the process of “finding” the other base unit, before the more precise positioning commands are commenced using the null-position photosensor. For example, without an omnidirectional sensor on the base units, if the second base unit's null-position photosensor is pointing away from the first base unit at the moment the first base unit's rotating fan beam strikes the second base unit, then that null-position photosensor (which does not extend 360 degrees around the base unit) would not be aware of that fan beam striking the second base unit, so valuable time would be lost, waiting for the next attempt. (Both base units rotate their fan beams—along with their null-position photosensors—about a vertical axis, so that the fan beams can point at any azimuth angle on the jobsite.)